Firefighters cleared debris Thursday after an explosion and fire in a five-story building the Chinatown section of New York City. / Bebeto Matthews, AP

by Natalie DiBlasio and Michael Winter, USA TODAY

by Natalie DiBlasio and Michael Winter, USA TODAY

An explosion and fire in a building in New York City's Chinatown injured 12 people, including four firefighters, the Associated Press reported Thursday afternoon.

The 12:45 p.m. ET blast caused the partial collapse of the first floor, said Assistant Chief Robert Boyce. The cause was not immediately known.

The New York Daily News cited an apparent natural gas explosion. NBC News, citing an unidentified law enforcement official, said the blast may have been caused by a severed gas line in the basement. WABC-TV reported that the rear of the building may have been under construction.

The five-story building includes commercial spaces with apartments above. The New York Post reported the explosion occurred in the back of a beauty salon.

Building resident Tszkan Cheung told AP he heard a "boom, like a bombing, like an earthquake." He saw firefighters carrying out a woman with a severely damaged leg.

Three of the injured were hospitalized in serious condition,but none were firefighters, AP said. The Daily News and the Post said the three were in critical condition. Each paper reported at least nine injuries.

NBC said the most seriously injured were on the second and third floors.

Boyce told the Post there were "existing code violations for this building and we are looking into that." He did not elaborate.